It is oftentimes necessary to sense an angular relationship between two or more units in order to achieve a desired end. Such is the case, for example, where it is necessary to know the angular position of a rotor element relative to a stator element and/or where it is necessary to know the angular displacement between two rotor elements both of which are rotatable with respect to a stator element.
In the case of a motor vehicle such as an automobile, for example, a steering wheel, when rotated, applies a rotative force or torque to a steering shaft, and both the steering wheel and the steering shaft are rotatable with respect to the frame of the vehicle having the steerable (normally front) wheels mounted thereon so that rotation of the steering wheel results in turning of the steerable wheels.
A mechanical arrangement has been, and is, used to cause turning of the steerable wheels in response to rotation of the steering wheel, and a hydraulic system has also been, and is, utilized to cause turning of the steerable wheels with operation of the hydraulic system being initiated in response to rotation of the steering wheel.
Thus, while both mechanical systems and hydraulic systems have been heretofore utilized to control turning of the steerable wheels of a motor vehicle such as an automobile, no system now exists that allows the driver of such a vehicle to more fully control turning of such a vehicle while being assisted in effecting the desired turn by an electrically powered unit.
Power assist has been utilized in other wheeled vehicles, such as, for example, in conjunction with a wheelchair to assist in propelling the wheelchair (see, for example, U.S. Pat. Nos. 4,050,533, 4,125,169 and 4,422,515).
A power assisted wheelchair using capacitive sensing to detect angular displacement between the hand rim and drive wheel is also shown and described in pending U.S. patent application Ser. No. 07/612,824, owned by the assignee of this invention. In the capacitive sensing embodiment shown in pending U.S. patent application Ser. No. 07/612,824, power is provided through mechanical slip rings to a hub mounted unit that includes an oscillator and amplifier and the output is also coupled from the unit through mechanical slip rings.
Various capacitive sensing units are also shown and described in U.S. Pat. No. 3,012,192, including sensing of displacement.